Well that is what the "noodles" are for apparently. 14mm requires more heat, meaning it can blister and bubble etc.
Either way? tbh? if he is doing this on a budget he can absolutely forget hard line, and I will tell you why. It will cost him £100 to get set up before he even buys a single fitting or piece of tube. The correct (heat controlled) heat gun isn't cheap, and a radius kit will cost £50 or so. Then you need a de-burring tool (only about £6 but you still need it) and so on.
That is mainly why I am not using that hard line tubing in mine. Oh and a good cutter too costs a few quid.
All you need with soft tubing is a good cutter. A proper hose cutter. Mine was about a tenner, IIRC.